Automated data storage libraries are known for providing cost effective access to large quantities of stored data. In an automated data storage library, numerous storage slots, or cells, are arrayed within the library and are used to hold data storage media, such as magnetic tape cartridges or cassettes. (The term "media" used herein refers to any portable housing structure containing any type of data storage media.)
In a conventional automated data storage library, the storage slots are arranged in a planar or cylindrical orthogonal arrangement of rows and columns, forming a "wall" of storage slots for holding data storage media. An accessor, furnished with one or more pickers, is a robotic device which moves along a guideway in a horizontal motion, or about a pivot in a rotary motion, and moves vertically to access the various storage slots with the picker, and transports selected data storage media amongst the storage slots and one or more drive units, which read and/or write data on the data storage media. To double the storage capacity, two "walls" of storage slots may be provided on either side of the accessor.
Libraries also typically contain input/output stations or ports through which an operator may pass data storage media to be added to the library and through which the accessor may pass data storage media to be removed from the library.
The operation of the accessor is typically under the direct control of a library manager, which is a programmed data processing controller typically situated in the library. A library manager typically comprises a micro-processor, including a database such as memory or a disk drive, and input/output adapters, such as SCSI ports. The disk drive typically stores the programs (microcode) which cause the manager to operate the library, and which include information indicating the characteristics of the particular library. The programs for the library manager may be installed or updated by a typical input device, such as a CD-ROM optical drive. The library manager is interconnected with one or more host computer systems, such as a mainframe or network computer, which issues commands to the library. The library may conventionally be arranged to retrieve and store data for a variety of hosts, often connected to the library over the same network. The host typically commands the library to retrieve a selected data storage media and deliver the data storage media to a data storage drive of the library.
The drive units may be directly interconnected with the host(s) over host/drive interfaces and, after a data storage media is delivered to a drive unit, it typically searches for, and reads selected data from or writes data to the selected data storage media in response to commands from the host. Each drive unit typically includes a drive and a controller for operating the drive. One example of a drive unit arrangement employing a single controller for operating a plurality of magnetic tape cartridge drives is the IBM 3590 Model A50 Data Storage Subsystem.
A number of different companies manufacture automated data storage libraries today, each model displaying various different features. One example is the IBM 3494 Data Storage Library, which stores magnetic tape cartridges, and employs IBM 3590 Data Storage Drives.
The incorporated Basham et al. U.S. Patent Application describes a method for formatting data storage cartridges to various capacities, called flexible capacity scaling, as employed, for example, with an IBM 3590 Data Storage Drive and IBM 3590 magnetic tape data storage media. Basham et al. describes the tape as a multi-track linear data storage media, which may have data blocks recorded in bi-directional serpentine patterns. Fixed capacity scaling, rather than storing the data blocks on several tracks or track groups sweeping the entire length of the tape, is the congregation of the data on all tracks of the tape near the beginning of the tape. Flexible capacity scaling stores the data blocks on a multi-track tape using a hybrid serpentine pattern, comprising separate sets of serpentine patterns along the length of the tape. Flexible capacity scaling is defined as the arrangement of the data blocks in a continuous configuration of multiple adjacent stacked serpentine patterns. The configuration is continuous in that sequential access to all data blocks is possible without advancing the tape to skip over any regions intervening between adjacent ones of the ordered data blocks.
As described in Basham et al., the fixed capacity scaling or the flexible capacity scaling of a tape is accomplished by the drive controller operating the drive to pre-format a tape, and is invisible to the host. By congregating the data blocks near the beginning of tape, tape head movement is advantageously restricted to only part of the tape and time consuming tape advancement operations are avoided in favor of small, relatively rapid operations to "vertically" align the tape head and data path and then indexing the tape head or switching to a different tape head.
In order to implement the above tape pre-formatting, the host must be programmed to command the drive to conduct pre-formatting of the tape.
Automated data storage libraries, however, as described above, operate with a variety of host processors, some of which may have different operating systems and application programs. For example, host processors may comprise an IBM personal computer, IBM model RISK System/6000 computer, IBM model AS/400 Advanced Systems computer, Sun workstation, HP workstation, IBM 3090 mainframe computer, or other suitable data processing apparatus. Thus, each of the different hosts may have to be provided with a special program in order to be enabled to command the drive to conduct pre-formatting of the tape.
Further, ones of the variety of hosts may have programming to communicate with data storage drives having differing interfaces, such as an IBM 3490-type of interface, an IBM 3490X-type of interface, an IBM 3590-type of interface, or an IBM 3590X-type of interface. The drive controller for the data storage drive of the IBM 3590 Model A50 Data Storage Subsystem has the capability to communicate in the protocol of ones of such a plurality of interfaces, and may be switched in an initialization process. However, in an automated data storage library, it may not be possible to dedicate a data storage drive to a single host.